The general objectives of the San Francisco Men's Health Study (SFMHS) are: (a) To better understand the natural history of HIV infection (b) To determine the risk factors and appropriate interventions to limit the spread of the disease and (c) To characterize any biologic or environmental factors that will alter the natural history of the disease (e.g., either limit or accelerate the morbidity and mortality associated with infection) in this population. The specific objectives of the SFMHS are: (1) To continue to study the natural history of HIV infection among a population of homosexual/bisexual men who have been enrolled in the SFMHS since 1983, specifically by collecting demographic, socio-cultural and self-reported behavioral data and statistically correlating these data with physical examination findings, HIV antibody status, immunologic and hematologic parameters and the presence of antibodies to other viruses. (2) To determine the rate of disease progression by comparing laboratory findings (HLA-type, CBC, SMA-12), immunologic parameters (by flow cytometry), physical examinations, and electromechanical findings (EEG, EKG, MRI, CAT, nerve conduction studies, radiographic findings) with behavioral risk factors and demographic characteristics. (3) To determine the rate of seroconversion among sexually active participants and to determine those behaviors which may alter the rate of seroconversion. (4) To determine the nature and extent of co-infections among sexually active homosexual men and their impact on the natural history of HIV infection.N01CP85604 The purpose of this project is to attain (nonprofessional), managerial, and clerical support for epidemiologic studies of cancer risk following radiation and related exposures. The contractor functions in a supportive role carrying out specific tasks and does not engage in independent research. All phases of support services are supplied including preparing data collection forms, preparing abstraction and interviewing manuals, conducting field studies, obtaining death certificates, locating populations for vital status determination, assessing exposure information, and creating and manipulating data files.